It is now prevalent in satellite microwave communications systems for the such systems to process multiple channels. This requires the combination or separation of the channels either for transmission or for processing after acquisition. This function is usually accomplished by means of a multiplexer. The typical multiplexer consists of a series of input waveguides generally including filter elements connected to a waveguide manifold through ports or irises. Each of the filters is tuned and the irises designed for maximum efficiency of the overall system.
In order to obtain optimum performance of the multiplexer, while minimizing losses, the internal impedance of the various components must be closely matched. This process of tuning the system requires the balancing of hundreds of variables many of which are extremely sensitive because of the high frequency environment. The design of these components has, therefore, become a difficult technological challenge. Although the optimization problem can be diminished through the use of various design techniques, because of the inherent limitations of manufacturing tolerances, the design of the these components ultimately relies on a trial and error process in which multiplexers are constructed, tested, modified, tested and gradually optimized in this manner. There are limits however, to the number of iterations which can be employed with constructive results.
It is a purpose of this invention to provide a multiplexer system and method of adjustment that allows a final adjustment of the impedance of the manifold to tune the overall system.
One means in the prior art for providing a final tuning step involves the insertion of tuning screws extending through the structure of the microwave filters, as shown in U.S. Pat. No. 4,614,920. A series of holes are drilled through the outer wall of the filter and screws are screwed in place to create adjustable perturbations on the inner surface of the associated filter waveguide cavity. This adjusting screw method, when applied to a tuning section as constructed in the manifold of this invention, creates undesirable reduction of power handling and contact problems leading to is possible generation of passive inter-modulation products (PIMS).
A waveguide system using a threaded rod protruding into a waveguide cavity for the purpose of fine tuning the impedance matching adjustment of the waveguide is shown in U.S. Pat. No. 4,200,847. This configuration also creates undesirable power handling and PIMS conditions.
It is a purpose of this invention to simulate the protrusions of the tuning screw without the need to fracture the wall of the waveguide and thereby avoid these problems.